1. Field of the Invention
The invention relates to a process for the wireless transmission of data to a traffic center for the purpose of assessing traffic in segments of a road network. The data are collected in a plurality of vehicles (floating cars) that travel in traffic and are equipped with sensor systems for data collection. The invention also relates to a device to implement this process.
2. Description of the Prior Art
Various methods are known for the metrological collection of data for traffic assessment in segments of a road network. Often, stationary or fixed sensors installed at roadside such, for example as induction loops, are used at especially critical locations to measure technical traffic variables, such as the number of vehicles passing during a given time period or the average speed of these vehicles. However, installing stationary sensors such as those disclosed in U.S. Pat. No. 5,317,311 at roadside or in the road surface is expensive, as is the maintenance of such sensors. As a rule, such sensors transmit current measurement data to a traffic center for further assessment at regular intervals.
Recently, there has been discussion and testing of processes in which data measurement for traffic assessment is conducted in the vehicles taking part in traffic. The vehicles used for this purpose are equipped with sensors. Such sensor vehicles are also called "floating cars." This concept of data collection presupposes wireless communications for data transfer between the floating cars and a traffic center. Preferably, data transfer is carried out via radio. Due to the limited capacity of the broadcast channels, such communications must, for technical as well as economic reasons, be limited, to the greatest possible extent, to the necessary minimum. Instead of constantly maintaining radio contact, a typical application of the floating car concept disclosed, for example in DE 195 13 640 simply transmits the most recent measurement data at regular intervals. These data include, in particular, the time of day, the location and speed of the vehicle and, as applicable, other measurement variables on the vehicle surroundings, e.g., fog, rain or black ice. Such a chronological chain of individual data is described hereinafter as the "driving profile."
However, this known process is not completely satisfactory. It has the disadvantage that, despite data reduction, measurement data with little informative value are frequently transmitted. The reporting behavior of each vehicle is controlled purely chronologically, for example, and is not directly influenced by the usefulness of the transmitted data for the purpose of traffic assessment. The individual floating cars report their data regardless of whether they happen to be located on a completely empty road or in heavy traffic or in a zone where traffic has been disrupted by a recent accident. Since the primary goal of data collection for traffic assessment is to detect traffic disruptions, reports of non-disrupted traffic contribute only slightly to this goal.